HandlerThread（本质是Thread）
1.减轻主线程的压力，提高UI的流畅度
2.可以处理多个任务，开启一个线程起到多个线程的作用（looper共享）
public class HandlerThread extends Thread {
int mPriority;
Looper mLooper;
public HandlerThread(String name) {
super(name);
mPriority = Process.THREAD_PRIORITY_DEFAULT;
}
public HandlerThread(String name, int priority) {
super(name);
mPriority = priority;
}
//run方法里面的的内容在子线程中执行
public void run() {
mTid = Process.myTid();
Looper.prepare(); //创建Looper放到ThreadLocal<Looper>里面
synchronized (this) {
//从ThreadLocal<Looper>中获取当前子线程的Looper
mLooper = Looper.myLooper();
notifyAll();
}
Process.setThreadPriority(mPriority);
onLooperPrepared();
Looper.loop();
mTid = -1;
}
/**
* 如果Looper没有创建好，会阻塞在这里
*/
public Looper getLooper() {
synchronized (this) {
while (isAlive() && mLooper == null) {
try {
wait();
} catch (InterruptedException e) {
}
}
}
return mLooper;
}
public boolean quit() {
Looper looper = getLooper();
if (looper != null) {
looper.quit();
return true;
}
return false;
}
}
HandlerThread与Camera的能够Looper共享
需求：
打开相机
预览回调（编码）
异步任务的Looper，使用的MainLooper
public class AsyncTaskActivity extends Activity
implements Callback {
static final String TAG = "AsyncTaskActivity";
Camera mCamera;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
byte[] buffers;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handler_thread2);
surfaceView = (SurfaceView) findViewById(R.id.surface_view);
surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(this);
}
class MyTask extends AsyncTask<Void, Void, Void> implements PreviewCallback{
@Override
protected Void doInBackground(Void... params) {
//子线程中打开
Log.d(TAG, Thread.currentThread().getName() + "_open");
mCamera = Camera.open(CameraInfo.CAMERA_FACING_BACK);
try {
mCamera.setPreviewDisplay(surfaceHolder);
} catch (IOException e) {
e.printStackTrace();
}
Camera.Parameters parameters = mCamera.getParameters();
//设置相机参数
parameters.setPreviewSize(480, 320); //预览画面宽高
mCamera.setParameters(parameters);
//获取预览图像数据
buffers = new byte[480 * 320 * 4];
mCamera.addCallbackBuffer(buffers);
mCamera.setPreviewCallbackWithBuffer(this);
mCamera.startPreview();
Log.d(TAG, Thread.currentThread().getName()+ "_doInBackground");
return null;
}
//画面预览的回调
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
if(mCamera != null){
mCamera.addCallbackBuffer(buffers);
//主线程执行
Log.d(TAG, Thread.currentThread().getName()+ "_onPreviewFrame");
}
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
new MyTask().execute();
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format,
int width, int height) {
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
}
onPreviewFrame方法的回调实在相机类(Camera)里面的EventHandler.handleMessage方法中执行，onPreviewFrame方法调用跟EventHandler.handleMessage在同一个线程里面，而EventHandler.handleMessage调用所在线程是由Looper所在线程决定。
由于在上面的代码中没有调用Looper.prepare()， 结合Camera的构造函数可以知道会进入else if这个条件里面，此时Looper是在主线程的，因此上面代码中的onPreviewFrame方法在主线程调用的。
Camera(int cameraId) {
...
Looper looper;
//Looper.myLooper()不为空前提是调用了Looper.prepare()方法
if ((looper = Looper.myLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else if ((looper = Looper.getMainLooper()) != null) {//主线程
mEventHandler = new EventHandler(this, looper);
} else {
mEventHandler = null;
}
}
public class HandlerThreadActivity2 extends Activity implements Callback {
static final String TAG = "jason";
Camera mCamera;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
byte[] buffers;
HandlerThread mHandlerThread = new HandlerThread("my_handlerthread");
Handler subHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handler_thread2);
surfaceView = (SurfaceView) findViewById(R.id.surface_view);
surfaceHolder = surfaceView.getHolder();
surfaceHolder.addCallback(this);
}
class MyTask implements Runnable, PreviewCallback{
@Override
public void run() {
//打开相机
//子线程中打开
Log.d("jason", Thread.currentThread().getName() + "_open");
mCamera = Camera.open(CameraInfo.CAMERA_FACING_BACK);
try {
mCamera.setPreviewDisplay(surfaceHolder);
} catch (IOException e) {
e.printStackTrace();
}
Camera.Parameters parameters = mCamera.getParameters();
//设置相机参数
parameters.setPreviewSize(480, 320); //预览画面宽高
mCamera.setParameters(parameters);
//获取预览图像数据
buffers = new byte[480 * 320 * 4];
mCamera.addCallbackBuffer(buffers);
mCamera.setPreviewCallbackWithBuffer(this);
mCamera.startPreview();
Log.d(TAG, Thread.currentThread().getName()+ "_run");
}
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
if(mCamera != null){
mCamera.addCallbackBuffer(buffers);
//子线程执行
Log.d(TAG, Thread.currentThread().getName()+ "_onPreviewFrame");
}
}
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
mHandlerThread.start();
subHandler = new Handler(mHandlerThread.getLooper());
subHandler.post(new MyTask());
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format,
int width, int height) {
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
}
}
